Cardiotonic agents have been used for the treatment of heart failure for some time with digitalis continuing to be one of the principle pharmacologic agents used for this purpose, although the cardiac glycosides as a class do have some limitations. The output is regulated by the integration of the contractile state of the heart and the dynamics of the periphery circulatory system. When the heart fails, the primary problem is impairment of ventricular myocardial contractility which results in inadequate cardiac output to meet the metabolic and circulatory demands of the body. Effective therapy of heart failure is accomplished by either enhancing the contractile state of the heart with positive inotropic agents, or by adjusting the peripheral circulatory state with pheripheral vasodilators. Agents which stimulate myocardial contractility are of considerable value in the treatment of heart failure. Conventional therapy for heart failure has been the use of digitalis preparations which are the only orally effective inotropic drugs available for use in the treatment of this condition. However, their peripheral vascular effects are undesirable. Sympathomimetic amines are the other major class of cardiac stimulants which are used for the treatment of heart failure. The use of these agents is likewise limited, because they are not fully effective when administered orally and because of undesirable peripheral vasoconstrictor action. Currently, dobutamine and dopamine are the sympathomimetic agents which are primarily used for heart failure.
A promising inotropic agent which has been studied recently is the bipyridyl analog amrinone having the following formula: ##STR2##
See Drug's of the Future, 4, 245 (1979), and A. E. Parah, et at, Life Sci., 22, 1139 (1978). In pentobarbital induced heart failure in dogs, amrinone caused an increase in both contractile force and cardiac output. However, experiments in dogs with experimentally induced ischemia indicate that amrinone and isoproterenol may increase acute ischemia and myocardial injury which could possibly limit the use of amrinone in heart failure patients with acute myocardial ischemia.
The compound of the following formula ##STR3## administered intravenously was found to increase myocardial contractile force and heart rate and decrease blood pressure in anesthetized dogs. The compound produced greater hemodynamic effects in dogs with experimentally induced heart failure that than in normal dogs, as reported by C. P. Hsieh, et al, Fed. Proc. Fed. Am. Soc. Exp. Biol., 39, 1106 (1980); and L. E. Roebel, et al, Pharmacologist, 22, 287 (1980).